as long as engulfing flames of a dragonknight is provided (which should be in good guild raids) MSA flamestaff is best on slot. lightning staff was better pre dragons bones, since all the lighting damage provided a lot of offbalance and the cp passive exploiter increased damage against offbalanced enemies by 10%. now offbalance is up 25% at most, which makes it hard to rely on that. thats why everybody changed to flamestaves on backbar, especially with the buff from engulfing flames. nirnhoned is BiS for aoe fights, since enchants cant proc on multiple enemies, because they have a cooldown. therefore the gained 200 spelldamage from nirn is better, since all enemies are affected. for single target damage infused is better, since it actually makes up for those 200 spelldamage with a high uptime of the berserker enchant.
so thats why double inferno is best atm with nirn for aoe and infused for single target.